Paramagnetic microwave power detector wherein interacting electric and magnetic fields exist in a single plane



March 26, 1968 H. J. JURETSCHKE ET AL 3,375,442

EAHAMAGNETIC MICROWAVE POWER DETECTOR WHEREIN INTERACTING ELECTRIC ANDMAGNETIC FIELDS EXIST IN A SINGLE PLANE Filed Dec. 15, 1962 INVENTORJ.fiCLLMl/T J rive: 766/ 065 BY W44 me 4 4 un t sweete 7 3,375,442 VPARAMAGNETIC MICROWAVE POWER DE TECT R INTERAETING, ELEC- TRIC ANDMAGNETIC FIELDS. EXIST IN A SINGLE PLANE H I v Helhniit J. Jnretc hke,Brcoklyn, ,and Walter Egan, Richmond Hill, N.Y., assi nors', h'y niesnassignments, to the United States of America as represented'by theSecretary of the Navy p, Contiiiuatioii iii-p'ai't 6f apfrlicat'io'liSer. No. 41,710, July 8, 1960. This application D'e'c. '13, 1962; Ser.No; 244,534 r 11 Claims; (Cl. 324 -95) This application is acontinuation-impart of application Ser. No. 41,710, filed July 8, 1960and now aban-- doned;

This invention relates to a microwave energy detector and especially toa detector which utilizes the electron spin resonance condition ofelectrically conductive, strongly paramagnetic materials to detectmicrowave energy.

The detection and measurement of microwave energy or power is frequentlyrequired in fields such as radar and microwave communications. It istherefore desirable to have a device which is capable of detecting andmeasuring microwave power; The present invention provides a microwavedetector which is of simple construction, rugged,- and inexpensive, canyield absolute power measurements; can be used at all frequencies, andis linear with respect to microwave power.

Furthermore, the invention can be used to measure frequency and magneticfield strength. It may also be employed for frequency control and powercontrol.

The objects and advantages of the present invention are accomplished byplacing a thin film of electrically conductive, strongly paramagneticmaterial in a region of microwave field where the electric fieldcomponent is weak and the magnetic field component in the plane of filmis strong. A D.C., or timednvariant, magnetic field is set up in theplane of the film at right angles, preferably, to the microwave magneticfield component, the D.C. magnetic field beingof such strength as tocause electron spin resonance in the film. A pair of spaced electrodesare connected in the film, preferably along the direction of themicrowave magnetic field.

The interaction of the microwave and D.C. magnetic fields generates anelectric field the film in the direction of the electrodes; Thiselectric field has an average, or D.C. component, and produces a DC.voltage across the electrodes. The DIG; voltage can be amplified andapplied to an indicator, such as an out-put meter-,- calibrated toprovide a reading of the microwave power,

An object of this invent-ion is to measure microwave energy.

. Another object is to provide a simple, rugged and inexpensive devicefor measuring microwave energy Yet anothero'bject is to provide a devicefor the measurement of microwave power, the device being linear andusable at all microwave frequencies. p

A further object is to provide a device which can be adapted to measuremicrowave fr qtiaiey.

Still another object is to provide a device -whicli can be adapted tomeasure magnetic field strength Other objects and many of the attendantadvantages of this invention will be readily appreciated as the samebecomes better understood by reference t6 the following detaileddescription when considered in connection with the accompanying drawingswherein the single figure illustrates an embodiment of the invention;

A waveguide 12, which is partially broken away, is shown in the figure;it is to be understood that the wave- 3,375,442 we M rie 5% guide 12 iscoupled to the source of microwaye energy which is to be measured. Athin film 14 of electrically conductive, strongly paramagnetic materialcoated on an insulator material is mounted on an inside wall of theWaveguide 12 so that the film 14 faces the interior of the waveguide 12.7 e

The fil'ni 14 should be no. more than approximatel 1000 A.,corresponding o the order or the skin depth: The film thicknessmust beless than the'skifi depth idff the microwave energy which, is beingdetected, since if the him is thicker; the part of the filni notpenetrated by the microwaves acts as a short on the D.C. electric fieldinduced in the film;

(Hereinafter, seen a filin' will be re ferred to as a thin film) Thematerial used for the film 14 is an electrically conductive, stronglyparamagnetic material such as the material nickel above its Curietemperature or the electrically conductive material gadoliniur'n, forexample. The ter' strongly par magheae indicates that an appreciablemagnetizatibn is required for the system to operate, for eiiample, thatthe relative permeability of the material be greater than unity byperhaps 10% or more. The gadclinium, which is ferro= magnetic below roomtemperature and paramagnetic at elevated temperatures, can be employedat a tempera ture of about 50 (3., for escape, ifit is desired that itbe used in its paramagnetic state. insulating material which supportsthe film 14 maybe a glass plate about 3 mils thick, for eiani'ple.

A D.C. magnetic field, H is set up by means such as an electromagaet orwhich an fragmented polepiece segments 15 and 17 are shown in thefig'ure)' so that the field eXists in the plane of the film 14. The film14 is locatedwithiri the waveguide 12 so that the micro- Wave magneticfield, H is also in the plane of the film 14 at right angles to the D.C.magnetic field. The microwav'e' electric field, E,-,-,, is then in thesame direction as the D.C. magnetic field, H This is indicated arrows inthe figure. The location of the filin 14 'should also be at a point atwhich the microwave electric field, E is weak and the magnetic microwavefield, H is strong; For example; the film 14 may be placed one quarterwavelength from the short termiriatiiig a rectangular waveguideprbpagating in the TE' mode.

A pair of electrodes 16 and 18 are affixed to the film 14 in thedirection 6f polarization, if it eiiists, and output leads 20 and 22-aresoldered to the electrodes 16 and 18 with low thermal solder. The leads20 and 2 2 arebic iught out of the waveguide 12 through small holes 24'and 26 and fed to an amplifier 28, whose oiit-put, in turn, is appliedto an outpiit indicator 30;

If the device is being employed to measure microwave power, the energytc be ineasiired is propagated through the waveguide 1 2 is the film14.;The Strength of the D.C. magnetic field, H is varied until a maximumoutput Signal is ob'taiiied. This occurs in theneighborhood of themagneticspin resonance peak, A D.C. electric field, E is set up in thepane er the film 14am pr duces a D.C. voltage acrossth'e' electrodes 16and 18 which is' directly proportional to the incident microwave power.It is belieVed that the D.C. electric i 'nal Pr Odliced is a result of aHall effect interaction between the microwave components of themagnetization and the eddy currents in the filmgand a magneto-resistancetfet dire to variaticn in resistance of the filrn resulting item theyai'iation in magnetization of the filin as the microwave field varies.The variation in resistance of the filrn affects the strength of thesignal induced in the film by the D.C. maghetic field, Theseinteractions provide an average, or steadystate, electric field. If the"microwave energy is continuous, the D.C. output signal is constant; ifthe microwave energy is pulsed, the D.C. oiitput signal iscorrespondingly pulsed.

The D.C. output voltage is applied to an'amplifier 28, which is a D.C.amplifier if the D.C. output signal is steady and an A.C. amplifier ifthe D.C. output signal is pulsed. The output of the amplifier 28 is thenfed to an output indicator 30 which may be a voltmeter or oscilloscopecalibrated to read in terms of power. Calibration may be accomplished bythe use of various microwave signals of known power, the frequency ofthe microwave signals and the D.C. magnetic field strength (H beingmaintained constant.

If his desired to employ the device to measure magnetic field strengths,the output indicator is calibrated in terms of magnetic field strengthby the use of magnetic fields (H of known strength and a microwavesignal in the waveguide 12 of fixed frequency and power.

Similarly, the device can be used as a frequency meter by calibratingthe output indicator in terms of frequency, an adjustable magnetic fieldstrength (H and fixed level microwave power being employed while themicrowave frequency is set at known values.

It should be apparent that the use of a waveguide is for the purpose ofconveniently propagating the microwave energy. If the microwave energyis propagated in another manner, e.g., through the air by means of amicrowave dish antenna, the thin film must be suitably located thereinin accordance with the magnetic and electric field orientations, asdescribed heretofore.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

We claim:

1. A device for the detection of microwave electromagnetic energycomprising, in combination:

a thin film of electrically conductive, strongly paramagnetic materiallocated within the electromagnetic field of said microwave energy at apoint where the magnetic component of the microwave field is strong andlies in the plane of said film, the electric component of the microwavefield also lying in the plane of said film;

means for establishing a time-invariant magnetic field in the plane ofsaid film at right angles to the microwave magnetic field, the strengthof said time-invariant magnetic field being sufiicient to produce acondition of magnetic spin resonance in said film; and

a pair of spaced electrodes in electrical contact with said film, thedirection of the spacing being the same as the direction of the D.C.electric field produced in said film by the interaction of the microwaveenergy with the time-invariant magnetic field.

2. A device as set forth in claim 1, further including means connectedto said electrodes for indicating the existence of a D.C. voltagebetween said electrodes.

3. A device for the detection of microwave electromagnetic energycomprising, in combination:

a thin film of electrically conductive, strongly paramagnetic materiallocated within the electromagnetic field of said microwave energy at apoint where the magnetic component of the microwave field is strong andlies in the plane of said film, the electric component of the microwavefield also lying in the plane of the film;

means for establishing a time-invariant magnetic field of adjustablestrength in the plane of said film at right angles to the microwavemagnetic field so that the strength of said time-invariant field can beadjusted to produce a condition of magnetic spin resonance in said film;and

a pair of spaced electrodes in electrical contact with said film, thedirection of the spacing being the same as the direction of theinteraction of the microwave energy with the time-invariant magneticfield.

4. A device as set forth in claim 3 further including means connected tosaid electrodes for indicating the existence of a D.C. voltage betweensaid electrodes.

5. A device for the detection of microwave electromagnetic energycomprising, in combination:

a waveguide for propagating said microwave energy;

a thin film of electrically conductive, strongly paramagnetic materiallocated within said waveguide at a point where the magnetic component ofthe microwave field is strong and lies in the plane of said film, theelectric component of the microwave field also lying in the plane ofsaid film;

means for establishing a time-invariant magnetic field in the plane ofsaid film at right angles to the microwave magnetic field, the strengthof said time-invariant magnetic field being sufiicient to produce acondition of magnetic spin resonance in said film;

a pair of spaced electrodes in electrical contact with said film, thedirection of the spacing being the same as the direction of the D.C.electric field produced in said film by the interaction of the microwaveenergy with the time-invariant field; and

means connected to said electrodes for indicating the existence of aD.C. voltage between said electrodes.

6. A device as set forth in claim 5, further including means to vary thestrength of said time-invariant magnetic field.

7. A device for the measurement of microwave electromagnetic energlycomprising, in combination:

a thin film of electrically conductive, strongly paramagnetic materiallocated within the electromagnetic field of said microwave energy at apoint where the magnetic component of the microwave field is strong andlies in the plane of said film, the electric component of the microwavefield also lying in the plane of the film;

means for establishing a time-invariant magnetic field in the plane ofsaid film at right angles to the microwave magnetic field, the strengthof said time-invariant magnetic field being sufiicient to produce acondition of magnetic spin resonance in said film;

' a pair of spaced electrodes in electrical contact with said film, thedirection of the spacing being the same as the direction of the D.C.electric field produced in I said film by the interaction of themicrowave energy with the time-invariant magnetic field;

an amplifier having an output and an input, the latter being connectedto said pair of electrodes;

and an output indicator connected to the output of said amplifier.

8. A device for the measurement of microwave electromagnetic energycomprising, in combination:

a thin film of electrically conductive, strongly paramagnetic materiallocated within the electromagnetic field of said microwave energy at apoint where the magnetic component of the microwave field is strong andlies in the plane of said film, the electric component of the microwavefield also lying in the plane of means for establishing a time-invariantmagnetic field of adjustable strength on the plane of said film at rightangles to the microwave magnetic field, the strength of saidtime-invariant magnetic field being suflicient to produce a condition ofmagnetic spin resonanoe in said film;

a pair of spaced electrodes in electrical contact with said film, thedirection of the spacing being the same as the direction of the D.C.electric field produced in said film by the interaction of the microwaveenergy with the time-invariant magnetic field;

an amplifier having an output and an input, the latter being connectedto said pair of electrodes;

and an output indicator connected to the output of said amplifier.

9. A method for the detection of microwave energy comprising the stepsof:

placing a thin film of electrically conductive, strongly paramagneticmaterial, having a pair of spaced electrodes in electrical contacttherewith, in a field of electromagnetic microwave energy, orientingsaid film so that the magnetic and electric components of the microwavefield lie in the plane of said film;

establishing a time-invariant magnetic field in the plane of said filmtransverse to the direction of the magnetic component of said microwavefield;

adjusting the strength of said time-invariant magnetic field until astate of electron spin resonance is attained in said film; and

placing spaced electrodes in electrical contact with said thin film, thedirection of spacing being the same as the direction of the DC. electricfield produced in said film by the interaction of the microwave energywith the time-invariant magnetic field.

10. A method for the detection of microwave energy comprising the stepsof:

placing a thin film of electrically conductive, strongly paramagneticmaterial, having a pair of spaced electrodes in electrical contacttherewith, in a field of electromagnetic microwave energy at a pointwhere the microwave magnetic component is strong and lies in the planeof the film, the electric component of the microwave field also lying inthe plane of the film;

establishing a time-invariant magnetic field in the plane of said filmtransverse to the direction of the magnetic component of said microwavefield;

adjusting the strength of said time-invariant magnetic field until astate of electron spin resonance is attained in said film; and

placing spaced electrodes in electrical contact with said thin film, thedirection of spacing being the same as the direction of the DC. electricfield produced in said film by the interaction of the microwave energywith the time-invariant magnetic field.

6 11. A method for the detection of microwave energy comprising thesteps of:

placing a thin film of electrically conductive, strongly paramagneticmaterial, having a pair of spaced electrodes in electrical contacttherewith, in a field of electromagnetic microwave energy at a pointwhere the microwave magnetic component is strong and lies in the planeof the film, the electric component of the microwave field also lying inthe plane of the film;

establishing a time invariant magnetic field in the plane of said filmtransverse to the direction of the magnetic component of said microwavefield.

adjusting the strength of said time-invariant magnetic field until amaximum D.C. electric field is produced in said film between said spacedelectrodes; and

placing spaced electrodes in electrical contact with said thin film, thedirection of spacing being the same as the direction of the D.C.electric field produced in said film by the interaction of the microwaveenergy with the time-invariant magnetic field.

References Cited UNITED STATES PATENTS 2,793,360 5/1957 Beaumont 340-3472,894,209 7/1959 Chodorow et a1 331-94 OTHER REFERENCES Egan, W. andJuretschke, H. J Detection of Ferromagnetic Resonance, Bull. Am. Phy.Soc., Ser. II, 3, 1958, page 194.

Sensiper, Samuel, Resonance Loss Properties of Ferrites in the 9KmnRegion, in Proceedings of the IRE, vol. 44, No. 10, October 1956, pp.1323-1342.

RUDOLPH V. ROLINEC, Primary Examiner. WALTER L. CARLSON, Examiner.

G. L. LETT, E. F. KARLSEN, Assistant Examiners.

1. A DEVICE FOR THE DETECTION OF MICROWAVE ELECTROMAGNETIC ENERGYCOMPRISING, IN COMBINATION: A THIN FILM OF ELECTRICALLY CONDUCTIVE,STRONGLY PARAMAGNETIC MATERIAL LOCATED WITHIN THE ELECTROMAGNETIC FIELDOF SAID MICROWAVE ENERGY AT A POINT WHERE THE MAGNETIC COMPONENT OF THEMICROWAVE FIELD IS STRONG AND LIES IN THE PLANE OF SAID FILM, THEELECTIC COMPONENT OF THE MICROWAVE FIELD ALSO LYING IN THE PLANE OF SAIDFILM; MEANS FOR ESTABLISHING A TIME-INVARIANT MAGNETIC FIELD IN THEPLANE OF SAID FILM AT RIGHT ANGLES TO THE MICROWAVE MAGNETIC FIELD, THESTRENGTH OF SAID TIME-INVARIANT MAGNETIC FIELD BEING SUFFICIENT TOPRODUCE A CONDITION OF MAGNETIC SPIN RESONANCE IN SAID FILM; AND A PAIROF SPACED ELECTRODES IN ELECTRICAL CONTACT WITH SAID FILM, THE DIRECTIONOF THE SPACING BEING THE SAME AS THE DIRECTION OF THE D.C. ELECTRICFIELD PRODUCED